# Low noise linear power supply schematics

#### bjornkarl

Joined Mar 14, 2021
8
I'm looking for a help in suggesting an appropriate circuit diagram for a very low noise linear power supply with output of 5.1VDC nominal. The load is varying between min 60 and max 120mA. I already have a 120VAC/10VA R-Core transformer with 12VAC output available and was thinking it could perhaps be used for this?

#### dl324

Joined Mar 30, 2015
13,119
Welcome to AAC!

With a 12VAC secondary and a 5.1V output voltage, you should have no problems with noise from a commercial linear voltage regulator. Unless your definition of very low noise is unreasonable.

#### bjornkarl

Joined Mar 14, 2021
8
Thanks Dennis! I have not been able to find a low power regulator such as this so I wanted to try and build one. But I'm not really good at circuit design

#### crutschow

Joined Mar 14, 2008
27,727
So how low is "low"?
That will allow better recommendations from us.

#### dl324

Joined Mar 30, 2015
13,119
I have not been able to find a low power regulator such as this so I wanted to try and build one. But I'm not really good at circuit design
From National Semiconductor:

Worst case load regulation is 1% for LM317A.

Since the regulator has a lot of headroom, you don't need much filter cap after the rectifier.

#### bjornkarl

Joined Mar 14, 2021
8
So how low is "low"?
That will allow better recommendations from us.

#### crutschow

Joined Mar 14, 2008
27,727
Well, I doubt you need that low a noise for your application, and standard low-noise IC regulator should suffice.
If you Google low-noise IC regulators you will get many hits (here's an example).
I would think that a power supply noise of a few tens of microvolts should be more than sufficient for you application.

#### dl324

Joined Mar 30, 2015
13,119
Thus many users buy the commercially availably Linear Power supply mentioned previously (at \$165).
Audiophiles make a number of outrageous claims. They say they can hear the difference between low oxygen copper and regular cables. Some even claim they can hear artifacts from wire splices.

Some people use carbon composition resistors because they say they like the distortion they introduce. Unfortunately, you need to be operating at over 100V to get that effect (as I recall).

#### bjornkarl

Joined Mar 14, 2021
8
Dennis,
I'm fully aware that some Audiophiles makes such claims. But not all of them. There is some people (like me) that would listen to music from a simple cheap device rather than not listening to music at all. But, in the case I have discussed here I have had the privilege of listening to the described DigiOne Streamer using a lower cost switched power supply and compared it to a clean power supply input using a Li-Ion battery pack. The difference was audibly very clear in favor of the battery supply. So, yes I may not need the ultra low noise as stated in the Linear Power supply referenced earlier (which I think is a unit that appeal to the more outrageous "demands"). Just looking for a solution that filters out clearly audible noise and which I can put together for substantially lower cost (and I do not wish to use a li-Ion pack as that requires constant attention to charge).

#### Papabravo

Joined Feb 24, 2006
16,799
Sorry, but gone are the days where a handful of discrete components on a breadboard or even a PCB can match the performance of an integrated component. It is really tough to out do the silicon makers.

#### bjornkarl

Joined Mar 14, 2021
8
Sorry, but gone are the days where a handful of discrete components on a breadboard or even a PCB can match the performance of an integrated component. It is really tough to out do the silicon makers.
I believe you are right! I will pursue a solution with a battery powerpack instead. A 20000mAh pack should give me about a day of use before needing a charge.

#### crutschow

Joined Mar 14, 2008
27,727
I will pursue a solution with a battery powerpack instead.
Why are you reversing gears and going with a battery, when a low-noise linear IC regulator would likely be more than adequate?

#### MrChips

Joined Oct 2, 2009
24,192
Just looking for a solution that filters out clearly audible noise...
Describe the noise. What are the frequency components of the noise?
Are you certain that the cause of the noise is the power supply?

#### Bordodynov

Joined May 20, 2015
2,906
See

#### bjornkarl

Joined Mar 14, 2021
8
Thank you for this! I will build and try it!

#### bjornkarl

Joined Mar 14, 2021
8
Why are you reversing gears and going with a battery, when a low-noise linear IC regulator would likely be more than adequate?
I'm not reversing gears entirely. I will put together a linear regulator and test side by side with a battery to see if I can hear the difference.

#### MrChips

Joined Oct 2, 2009
24,192
If a linear PSU has poor power line rejection the power line frequency of 60Hz and 120Hz (or 50Hz and 100Hz) will appear in the audio as hum.